"I named him as a suspect from Day One," said Sweeten, 51, the eldest of the victim's three children.
Neither Sweeten nor officials, however, could tell what the motive was.
Davis, in his 40s and a convicted sex offender, was arrested March 20 on unrelated charges not specified by the Gloucester County Prosecutor's Office, one day after Thirza Sweeten was found dead. Official documents give conflicting ages for him.
Davis became a suspect in the case early on, officials said Friday, as a result of an investigation that included more than two dozen interviews with neighbors.
While he has been held in the county jail since March, it wasn't until this week that physical evidence tests from the state police lab were returned, allegedly linking the suspect to the crime, Prosecutor Sean F. Dalton said. Davis is being held on $750,000 cash bail.
Davis' public defender, Frank Trosky, did not return a call seeking comment.
There was no evidence of theft from the home on South Delaware Avenue, officials said. They did not discuss any other possible motive.
Barry Sweeten, the only male sibling, said in an interview that a relative of Davis' had introduced the two and that Davis had visited the Sweeten home three or four times.
Sweeten said he was in a hospital March 19 when, according to a friend, Davis again visited his house.
"This wasn't a random act," Dalton said.
Authorities listed Davis' last known address as Swedesboro Avenue in Paulsboro. Davis is listed in the state's sex-offender registry for the sexual assault of two women in the late 1990s.
Members of Davis' family live near his home, Sweeten said. The Sweeten family has lived there since the early 1970s.
A transplant from England, Thirza Sweeten made a career as a nurse. She liked the Beatles, crocheting, and collecting cheap items from yard sales and flea markets, her son said.
She was a "penny pincher," he said, but for good reason: She was separated from her husband, Frank, for a period of time and had to support her three children.
Her husband had a drinking problem that caused him to be abusive at times; he died in 2005 from a failed liver, the son said. Thirza Sweeten was also a cancer survivor. Despite the circumstances, she always persevered, Barry Sweeten said.
In recent years, he said, he took his mother out of the house to take her mind off the grim memories of an abusive relationship. They visited the Cowtown Rodeo in Pilesgrove, one of her favorite places to scour for knickknacks to fill her home. That made her happy.
"My mom was known as a person to help people," Sweeten said.
She helped both neighbors and strangers, giving out money here and there, and was generous with her five grandchildren and five great-grandchildren, her son recalled.
His mother was about four feet tall and 110 pounds, Sweeten said, which is why she probably was defenseless against the person who killed her. She was found just outside her son's bedroom, he said. Sweeten said she likely was seeking refuge in the room, which has a lockable door.
Months after her death, Sweeten said, the loss has brought him and his siblings, Lisa and Pam, together.
Said Sweeten, pictures of his mother on either side of him: "It was a heinously senseless killing, for what?"
Contact Angelo Fichera at 856-779-3814 or firstname.lastname@example.org, or follow on Twitter @AJFichera.